The invention relates to fuel supply devices for internal combustion engines of the type comprising auxiliary throttle means located in the intake pipe upstream of operator an actuatable main throttle means, said auxiliary throttle means opening automatically and progressively in proportion to the increase in the air flow rate through the pipe. A source of fuel under pressure having a delivery circuit which opens into a portion of the intake pipe downstream of the main throttle means, the delivery circuit being controlled by at least one solenoid actuated valve and a metering system which is sensitive to the auxiliary throttle means, is provided with means supplying repeating pulse signals and is constructed to supply the solenoid valve with at least one valve energization signal per signal repetition period during a fraction of the period, the fraction being adjusted by the metering system.
Fuel supply devices of the above type are known in which the means delivering a succession of pulses includes a member which is continuously driven in rotation, typically by the engine: the period is then the duration of a 360.degree. rotation of the member.
The adjustment of the fraction of the rotation period (or of the fraction of a revolution) of the means determines the total time during which the valve is opened and consequently determines the flow rate of fuel injected into the intake pipe during aforementioned time interval.
The invention relates more particularly to devices of the aforementioned type wherein the source of fuel under pressure (for instance a fuel pump) has a delivery pipe provided with a pressure regulator comprising a discharge or relief valve which is biased toward opening by the delivery pressure and toward closure by the vacuum in a chamber connected by a connecting duct to that portion of the intake pipe between the two throttle means, the chamber being bounded by a diaphragm connected to the closure member of the valve. Thus, the pressure regulator maintains a fuel pressure which is substantially constant or varies in the same direction as the flow rate of air absorbed by the engine.
The regulator may comprise a discharge valve attached to the diaphragm, one surface of which is subjected to the pressure in that portion of the intake pipe between the two throttle means whereas the other surface is subjected to atmospheric pressure. Since the regulator is usually carried by the fuel tank, it is advantageous for the connection to atmosphere to be via the air vent of the fuel tank, but that arrangement has some disadvantages. The suction in the portion of the intake pipe between the two throttle means depends on the pressure drop produced by the air filter. If the air filter becomes clogged, the degree of vacuum increases and the discharge valve of the regulator is more strongly biased to closure, thus increasing the fuel pressure in the pump delivery pipe and consequently increasing the richness of the air-fuel mixture. The pressure in the fuel tank may vary, inter alia with temperature. More particularly, the pressure in the tank increases in hot weather. If the connection to atmosphere is via the tank, the pressure acting on the diaphragm increases and tends to close the discharge valve, thus further increasing the fuel pressure in the pump delivery pipe and consequently increasing the richness of the air-fuel mixture supplied to the engine.
To avoid excessive fuel consumption and atmospheric pollution by incompletely-burnt exhaust gases, the flow rate of fuel introduced into the intake pipe should preferably be adjusted. An obvious method is to vary the time periods during which the fuel-injecting valve is opened. For this purpose, however, it is necessary to modify the metering system. This method is expensive and different modifications have to be made for each type of engine, so that it is impossible to use a standard system for all engines.
It is an object of the invention to provide a fuel supply device improved with respect to the prior-art devices. It is a more specific object to provide a device which has simple and inexpensive adjusting means so that a standard system can be used for a number of engine types, and can be used when the system is electronic.
According to an aspect of the invention, there is provided a fuel supply system of the afore-mentioned type in which adjustment is achieved by controlling the pressure of the injected fuel so as to obtain an air-fuel mixture having a satisfactory richness. The adjustment means can be designed so as to adapt the richness to a wide range of engine operating parameters, e.g. by using an electric signal supplied by a probe sensitive to an operating condition of the engine or to the richness of the fuel mixture.
More specifically, there is provided a fuel supply device of the afore-mentioned type, the source of fuel under pressure being provided with a pressure regulator comprising a relief valve which is biased toward opening by the fuel delivery pressure and toward closure by the vacuum in a chamber connected to a connected duct to that portion of the intake pipe between the two throttle means, the chamber being bounded by movable or deformable means, such as a diaphragm, to which the closure member of the valve is connected, wherein the connecting duct is connected to atmosphere by a passage provided with a second solenoid valve associated with an energizing electric circuit constructed to supply said second solenoid valve with repetitive excitation signals having a duration which varies in dependence on an engine operating parameter, so that the total time during which the second solenoid valve is opened during a predetermined time period depends on the value of said parameter.
Providing that a sufficient piping volume is left between the solenoid valve and the chamber bounded by the diaphragm, the average vacuum acting on the diaphragm is practically free from fluctuations at the solenoid-valve excitation frequency. A calibrated orifice is typically placed between the duct and atmosphere on the air path controlled by the solenoid valve, the flow cross-sectional area of the orifice being selected in dependence on the flow cross-section of the connection to the intake pipe compartment.
The circuit comprises a pick-up probe for determining the engine operating parameter, which may inter alia be a physical or chemical property of the exhaust gases (e.g. the CO or oxygen content) representative of the richness of the fuel-air mixture.
The invention will be more clearly understood from the following description of a device constituting an embodiment thereof, given by way of non-limitative example.